1. Field of the Invention
The present invention relates to an optical disc drive device that applies a focus servo and a tracking servo to drive an optical disc, and to a tilt correction device that corrects tilt of the optical disc.
2. Related Art
During playback and record operations of an optical disc, focus error signals and tracking error signals are detected and a focus servo and a tracking servo are applied to reduce the error signals. With the focus servo and the tracking servo, a focus actuator and a tracking actuator are driven.
In order to apply the focus servo and the tracking servo stably, it is preferable that the open loop gain does not deviate from a predetermined level assumed at design of the optical disc drive. In reality, however, due to variation in a return beam intensity of a return beam signal, there is a possibility that amplitudes (detection sensitivity) of the focus error signal and the tracking error signal at servo-OFF vary, and the open loop gain deviates from the predetermined value, so that it may be impossible to apply the servos stably.
There is also the problem that division process is required in order to control the detection sensitivities of the focus error signal and the tracking error signal to be constant, and as a result the scale of the hardware becomes large (see Japanese Patent Application Publication JP-A (Kokai) No. 2006-155891).
Similarly, when the tilt of the optical disks is corrected, a tilt error signal which is the output of the tilt sensor is detected, and a tilt servo is applied so as to reduce the tilt error signal. In this case too, since division process is required in order to control the detection sensitivity of the focus error signal and the tracking error signal to be constant, it would be difficult to reduce the scale of the hardware.